PURPOSE: To enable reduction of the generation of noise through shut-off of resonance noise in an intake air passage in a condition to keep suction efficiency at an excellent value, by a method wherein a rotary disc, being open to the intake air passage, is situated up a line from a throttle valve in the intake air passage in linkage with a suction cam shaft.

CONSTITUTION: A rotary disc 17, opening and closing an intake air passage 11, is situated up a line from a throttle valve 13 in the intake air passage 11. The rotary disc 17 is formed in the shape of a disc, a communicating hole 20 is formed in the shape of an arc of a circle along the circumferential direction of the rotary disc, and a central shaft 18 of the rotary disc is rotated in linkage with a cam shaft 9 for suction through a cable 19. This constitution causes the rotary disc 17 to rotate in linkage with the cam shaft 9 for suction, forces the communicating hole 20 of the rotary disc 17 to be positioned facing the intake air passage 11 during opening of a suction valve 7, and forces intake air to be sucked in a combustion chamber 4 through an intake air port 5. Meanwhile, during closing of the suction valve 7, the intake air passage 11 is shut off by a portion where the communicating hole 20 of the rotary disc 17 is absent. This constitution enables shut-off of resonance noise in the intake air passage 11 in a condition to keep suction efficiency at an excellent value.